Conventionally, various touch input devices which each detect a touch position and a press on an operation surface have been devised. For example, Patent Literature 1 discloses a resistive touch panel. The touch panel in Patent Literature 1 includes a first conductive film and a second conductive film including principal surfaces parallel to an operation surface, and the first conductive film and the second conductive film are disposed at an interval in a direction orthogonal to the principal surfaces. When the operation surface is pushed, the first conductive film and the second conductive film contact with each other at a pushed position. The touch input device in Patent Literature 1 detects a touch position based on a partial pressure at this touched position, and detects a press based on the partial pressure and a resistance.
Such a configuration and an operation need a switch circuit which switches a touch position detection circuit and a press detection circuit to the first conductive film and the second conductive film to connect. Further, according to the configuration of Patent Literature 1, if a first electrode film and a second electrode film do not contact, i.e., if the operation surface is not pushed to some degree, it is not possible to detect a position.
Meanwhile, conventionally, a touch input device whose position detection sensor and press detection sensor are formed by using different base members, and which employs a configuration obtained by overlaying the position detection sensor and the press detection sensor has also been devised. According to this configuration, the position detection sensor is connected to a touch position detection circuit, and the press detection sensor is connected to a press detection circuit, and therefore a switch circuit is not necessary. Further, according to this configuration, it is possible to detect a position even when an operation surface is softly touched.
In this regard, by using a capacitive position detection sensor as the position detection sensor, it is possible to detect a touch position based on a change in a capacitance. Even when the operation surface is softly touched, i.e., even when the operation surface is not strongly pushed, it is possible to detect a touch position.
Further, while such a position detection sensor is used, a piezoelectric sensor for which a piezoelectric film is used is used as the press detection sensor in some cases.    PTL 1: Japanese Patent Application Laid-Open No. 2000-283869.
However, a combination of the capacitive position detection sensor and the press detection sensor formed by the piezoelectric sensor causes a following problem.
Electric charges are regularly injected to the position detection sensor to enable the capacitive position detection sensor to measure a capacitance. This injection amount changes according to the capacitance, and therefore changes between the case when a dielectric such as a finger touches the operation surface and the case when the dielectric does not touch the operation surface.
When the position detection sensor and the press detection sensor are disposed close to each other, the press detection sensor and the position detection sensor are capacitively coupled. In this case, electric charges are produced in the press detection sensor due to an influence of part of the electric charges injected to the position detection sensor.
The press detection sensor formed by the piezoelectric sensor detects whether or not there is a press or a pressing force based on electric charges produced when a piezoelectric film is deformed by a press on the operation surface.
Hence, when electric charges produced by the influence of the electric charges of the position detection sensor are produced in the press detection sensor, the press detection sensor erroneously detects these electric charges as electric charges produced by the piezoelectric sensor in response to a press. Therefore, it is not possible to accurately detect a pressing amount in some cases.